The present disclosure relates generally to drilling systems and more particularly to downhole tools for sampling formation fluid.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Wells are generally drilled into a surface (land-based) location or ocean bed to recover natural deposits of oil and gas, as well as other natural resources that are trapped in geological formations in the Earth's crust. A well is often drilled using a drill bit attached to the lower end of a “drill string,” which includes drillpipe, a bottom hole assembly, and other components that facilitate turning the drill bit to create a borehole. Drilling fluid, or “mud,” is pumped down through the drill string to the drill bit during a drilling operation. The drilling fluid lubricates and cools the drill bit, and it carries drill cuttings back to the surface in an annulus between the drill string and the borehole wall.
For successful oil and gas exploration, it is desirable to have information about the subsurface formations that are penetrated by a borehole. For example, one aspect of standard formation evaluation relates to measurements of the formation pressure, formation permeability and the recovery of formation fluid samples. These measurements may be useful for predicting the economic value, the production capacity, and production lifetime of a subsurface formation. Formation fluid samples may be extracted from the well and evaluated in a laboratory to establish physical and chemical properties of the formation fluid. Such evaluation may include analyses of fluid viscosity, density, composition, gas/oil ratio (GOR), differential vaporization, PVT analysis, multi-stage separation tests, and so forth. Recovery of formation fluid samples, in order to perform such evaluations, may be accomplished using different types of downhole tools, which may be referred to as formation testers. Formation testing tools may use pumps to withdraw fluid from a formation for analysis within the tool or storing the fluid in a sample chamber for later analysis.
It is now recognized that, under certain conditions, formation testing tools may encounter difficulty in efficiently recovering formation fluid samples. For example, when the sampled formation fluid is highly compressible, a formation testing tool may expend available pumping energy just to compress and decompress the fluid sample in the tool, instead of moving the fluid sample through the tool. Therefore, there is a need for improved downhole formation testing tools and improved techniques for operating and controlling such tools so that such downhole formation testing tools are more reliable, efficient, and adaptable to various formation, borehole, and mud circulation conditions.